The present invention relates generally to high-energy lasers used as weapons and, more particularly, to chemical lasers, such as DF (deuterium fluoride) lasers, used as defensive tactical weapons to intercept airborne devices considered to be military threats, such as artillery rockets or artillery shells of various types. Although high-energy lasers have long been considered as the ultimate defensive weapon to in, destroy airborne threats before they reach their intended targets, prior to this invention no-one has made or even proposed a design for a chemical laser powerful enough to perform this function and yet compact enough to permit the weapon to be readily deployed and provide mobile protection for troops in the field.
The capability of high energy lasers to shoot down artillery rockets in mid-flight has been demonstrated by the US Army using a system referred to as the THEL ACTD (Tactical High Energy Laser Advanced Concept Technology Demonstrator). This system is housed in multiple cargo containers 8xe2x80x2xc3x978xe2x80x2xc3x9740xe2x80x2 (approximately 2.4 mxc3x972.4 mxc3x9712 m), and requires a massive concrete slab for operational stability. The needed chemical reactants, C2H4, NF3, D2, combustor helium and cavity helium, were all stored in separate high-pressure tanks. Reactant flowing from the tanks was controlled by large digital flow control valves. The valves used a helium supply and regulation system. As diluents and reactants are removed from their supply tanks, flow control is rendered more difficult as the tank pressure and temperature of the remaining fluid fall toward the critical point. For helium and D2, the density of the remaining gas increases and the expulsion efficiency is reduced. For C2H4 and NF3, the problem is much greater in that, during the blowdown process, the gases approach the critical temperature and pressure, and their density increases in a nonlinear fashion, leaving most of the gas in the tank. This results in a requirement for the tanks to be much larger than they would need to be for ideal gas behavior.
As blowdown of the tanks and expulsion of the gases continues, the compressibility of the non-ideal gases changes drastically, making flow control more difficult. If the temperature of the C2H4 is allowed to drop below the critical temperature in the supply lines, condensation to the liquid state can occur, which would lead to system failure. This difficulty necessitates thermal control of the supply tanks, reactant supply lines and valve bodies.
The helium diluent must be mixed with the combustor and cavity reactant in prescribed amounts before injection into the combustor and laser cavity. This necessitates incorporation of inline mixers downstream of the flow controllers, which increases system complexity. Unfortunately, the system""s manifold volume requirements, needed to properly sequence the flows consumes reactants that could otherwise be usefully employed for lasing.
Another difficulty inherent to the THEL ACTD system is that it utilizes 70% hydrogen peroxide (H2O2) to provide high temperature/high pressure motive steam for maintaining sub-atmospheric pressure in the lasing cavity. The H2O2 is stored in a large 2,000-gallon (approximately 7,500-liter) tank, and it has some very onerous handling requirements. The tank may be of stainless steel, but if so it must be emptied after approximately seven days of exposure. To be useful, the H2O2 storage tank must include a liner of appropriate material, such as teflon, and the valves must be of a special material, such as zirconium. In operation, the THEL ACTD hydrogen peroxide tank must be pressurized to 800 psia, using helium as the pressurizing gas. This arrangement not only requires a very large helium supply tank and pressure regulation system, but raises safety concerns that require the hydrogen peroxide tank to be depressurized when personnel are nearby. Repressurizing the large supply tank quickly depletes the helium supply.
THEL ACTD uses silver based catalyst decomposition engines to decompose H2O2. These decomposition engines must be operated at a temperature fixed by the thermochemistry of 70% peroxide. Unfortunately, the fixed temperature is insufficient, in many conditions, to result in an invisible plume. Moreover, the decomposition engines have proven to be unreliable to operate and expensive to manufacture. In the THEL ACTD system, twenty decomposition units were needed, each with its own on-off valves, pressure instrumentation, and temperature instrumentation. A failure of any decomposition unit causes the system to fail.
THEL ACTD is a large laser weapon demonstrator which cannot be easily moved from one site to another. It would be highly desirable to provide a mobile tactical high energy laser (MTHEL), preferably one that is about five times smaller in size and weight than the THEL ACTD, such that the laser could be easily moved and set up for operation in a matter of minutes instead of days. It would also be highly desirable to provide a mobile system that did not have the other disadvantages of the prior art, which were previously discussed. The present invention is directed to these ends.
The present invention resides in a mobile tactical high energy laser system that is small enough to be carried by a single transport vehicle, such as a large truck or in a modular configuration. Briefly, and in general terms, the system of the invention comprises a deuterium fluoride (DF) or hydrogen fluoride (HF) laser assembly, for generating a high energy laser beam, the laser assembly including a gain generator assembly, a heat exchanger and an ejector; a nitrogen trifluoride (NF3) supply coupled to the laser assembly; deuterium (D2) or hydrogen (H2) supply coupled to the laser assembly; a water supply coupled to supply cooling water to the laser assembly; a high pressure steam generator coupled to receive water from the heat exchanger of the laser assembly, and to provide steam to the ejector of the laser assembly; beam director optics, for directing the laser beam in a selected angular direction; and a vehicle on which all components of the high energy laser weapon system are mounted for operation and convenient transportation, the truck having a conventional engine.
More specifically, the water supply includes a water tank, a pump; and water lines connecting to supply cooling water from the water tank and pump to the gain generator assembly and the heat exchanger, and to carry water from the heat exchanger to the steam generator. In the presently preferred embodiment of the invention, the pump is powered by the conventional engine of the vehicle.
In accordance with one aspect of the invention, the high pressure steam generator includes a bipropellant combustion chamber; source of oxygen coupled to the combustion chamber; and a fuel pump coupled to a fuel tank for the conventional engine of the vehicle, to supply fuel to the combustion chamber. The conventional engine fuel, such as diesel oil, reacts with oxygen in the combustion chamber and produces heat that transforms water into high pressure steam.
In the preferred embodiment of the invention, the deuterium (D2) or hydrogen (H2) supply includes a first reactant-diluent mixture tank containing a mixture of deuterium (D2) or hydrogen (H2) heavily diluted with helium, whereby, the gas mixture behaves substantially like an ideal gas than it would if not diluted. Additionally, the system comprises a supply of nitrogen trifluoride (NF3) stored in a second reactant-diluent mixture tank, also heavily diluted with helium; and a supply of ethylene (C2H4) stored in a third reactant-diluent mixture tank and also heavily diluted with helium. The second and third reactant-diluent mixture tanks are also coupled to the gain generator assembly. The system also includes a fluorine generator coupled to the gain generator assembly to supply fluorine (F2) to the laser assembly for ignition purposes; and additional supply tanks for nitrogen fluoride (NF3) and hydrogen (H2) to the fluorine generator.
Ideally, the system also comprises four electrically actuated flow controllers connected between the gain generator assembly and the first, second and third helium-reactant mixture tanks, gaseous oxygen (O2) for the steam generator respectively, and four shut-off valves, each connected in series with a respective one of the flow controllers.
In accordance with another aspect of the invention, the laser assembly includes an optical cavity in which lasing takes place, and a fast beam shutter located within the optical cavity, and operable to suppress lasing on command.
The invention may also be defined in terms of a method for generating a high energy laser beam on a movable vehicle. The method comprises the steps of supplying fluorine to the laser assembly; supplying other reactant gases to a deuterium fluoride (DF) or hydrogen fluoride (HF) laser assembly; initiating lasing in an optical cavity in the laser assembly and outputting a high energy laser beam from the optical cavity; supplying cooling water to the laser assembly; recovering heated cooling water from the laser assembly; generating high pressure steam from the recovered cooling water and supplying the steam to an ejector component of the laser assembly; and directing the high energy laser beam in a selected angular direction.
More specifically, the step of supplying other reactant gases includes storing each reactant gas in a storage tank with a diluent gas, for ease of handling and to provide more ideal gas behavior, and controlling the flow of each reactant gas to the laser assembly with an electrically actuated flow controller. The storing step includes storing deuterium or hydrogen in a tank with helium as a diluent; storing ethylene in a tank with helium as a diluent; and storing nitrogen fluoride in a tank with helium as a diluent The method of the invention may also comprise actuating a fast beam shutter installed in the optical cavity of the laser assembly, to terminate lasing as rapidly as possible.
It will be appreciated from the foregoing summary that the present invention represents a significant advance in the field of high energy laser weapon systems. In particular, the present invention provides an easily movable high energy laser system assembled onto a single vehicle, and without the need to store and use hydrogen peroxide at high pressures. In addition, the system makes efficient use of water for cooling and steam generation, and employs readily available diesel fuel and oxygen to generate high pressure steam for use in the laser assembly ejector. Other aspects and advantages of the invention will become apparent from the following drawings, taken in conjunction with following more detailed description.